1. Field of the Invention
The present invention relates generally to a multi-hop relay cellular system. More particularly, the present invention relates to a method and apparatus for managing Connection Identifiers (CIDs) in a multi-hop relay Broadband Wireless Access (BWA) communication system.
2. Description of the Related Art
Provisioning of services with different Quality of Service (QoS) levels at about 100 Mbps to users is an active study area for a future-generation communication system called a 4th Generation (4G) communication system. Particularly, active research is on going in the area of mobility and high-speed, high-Quality of Service (QoS) services in BWA communication system such as Wireless Local Area Network (WLAN) and Wireless Metropolitan Area Network (WMAN). The Institute of Electrical and Electronics Engineers (IEEE) is a major driving force in this area as exemplified by 802.16d and IEEE 802.16e.
The IEEE 802.16d and IEEE 802.16e communication systems adopt Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access (OFDM/OFDMA) for physical channels. IEEE 802.16d considers only fixed Subscriber Stations (SSs), i.e. a single-cell structure with no regard to mobility of SSs. In contrast, IEEE 802.16e supports the SS′ mobility to the IEEE 802.16d communication system. Hereinafter, a Mobile SS is called an MS.
FIG. 1 illustrates the configuration of a typical BWA communication system.
Referring to FIG. 1, the BWA communication system is configured in a multi-cell structure. Specifically, it is comprised of cells 100 and 150, BSs 110 and 140 for managing cells 100 and 150, respectively, and a plurality of MSs 111, 113, 130, 151 and 153. Signaling is carried out in OFDM/OFDMA between BSs 110 and 140 and MSs 111, 113, 130, 151 and 153. Among MSs 111, 113, 130, 151 and 153, MS 130 is located in a cell boundary area between cells 100 and 150, i.e. in a handover region. When MS 130 moves to cell 150 managed by BS 140 during signal transmission/reception to/from BS 110, the serving BS of MS 130 changes from BS 110 to BS 140.
In the above BWA communication system (i.e: IEEE 802.16), the ranging channel is used as an uplink random access channel. Initial ranging, periodic ranging, and bandwidth request ranging are performed through the ranging channel. Particularly, the initial ranging is performed during network entry or when system information is lost, with the aim to acquire uplink synchronization. In the initial ranging, a BS calculates the Round Trip Delay (RTD) between the BS and an MS by accurately measuring the time of arrival of a ranging signal from the MS and notifies the MS of a timing offset corresponding to the RTD. The BS also allocates a primary management CID and a basic CID to the ranging-requesting MS, for use in network entry and control message transmission/reception.
In the initial ranging process in which the BS allocates the CIDs to the ranging-requesting MS, upon power-on, the MS first acquires system synchronization by receiving a downlink preamble from the BS. Being synchronized to system timing, the MS receives DL (Downlink)-MAP and Downlink Channel Descriptor (DCD) messages and acquires downlink channel characteristic information from the received messages. The MS then receives Uplink MAP (UL-MAP) and Uplink Channel Descriptor messages from the BS and acquires initial ranging opportunity information, uplink channel characteristic information, and initial ranging-associated parameters.
Once the MS acquires minimum uplink and downlink channel information required for communicating with the BS in this way, it performs a basic access procedure, i.e. ranging to the BS based on the acquired information. That is, the MS sends a Ranging Request (RNG-REQ) message to the BS and the BS replies with a Ranging Response (RNG-RSP) message.
Since this initial ranging process precedes registration to the BS, neither the BS nor the MS has connection-associated information. Therefore, the MS uses an initial ranging CID as its CID. The initial ranging CID is preset to a value (e.g. 0x0000), common to all MSs and thus it is not managed separately.
Besides the initial ranging CID, the BWA communication system uses a plurality of other CIDs listed in Table 1 below.
TABLE 1CIDValueInitial Ranging CID0x0000Basic CID0x0001~mPrimary Management CIDm + 1~2mTransport CID2m + 1~0xFE9FMulticast CID0xFEA0~0xFEFE
Referring to Table 1, the initial ranging CID is used for the MS to attempt an initial access to the BS during the initial ranging process, as stated before.
The CIDs other than the initial ranging CID can be classified into two types according to their allocation processes and meanings: management CID and data transport CID.
The basic CID and the primary management CID are management CIDs and the transport CID is a data transport CID. The management CIDs are allocated to the MS from the BS without complicated service negotiations or requirements during registration since the management CIDs are basically allocated to the MS for registration to the BS irrespective of the service that the MS uses.
The transport CID is allocated to the MS from the BS whenever the MS needs a new connection. The transport CID allocation takes place when specific service class requirements are fulfilled by negotiations. Now a description will be made of the functions of the CIDs illustrated in Table 1.
The basic CID is MS-specific. As long as a connection is maintained between the BS and the MS, the basic CID can be used instead of the Media Access Control (MAC) address of the MS. After the initial ranging, the MS and the BS exchange control messages using the basic CID.
The primary management CID is used during network entry. The network entry process, which starts with the initial ranging process, can be defined as a series of processes in which the MS registers its information with the BS, inclusive of MS registration, service negotiation, and Internet Protocol (IP) address allocation. The BS identifies the MS by the primary management CID during the network entry process and significant control messages are sent/received using the primary management CID during communications between the BS and the MS. As with the basic CID, the primary management CID is kept for the MS as long as the connection is maintained between the MS and the BS.
The transport CID is used for actual service data transmission/reception. Upon completion of the network entry, the MS requests a service to the BS and the BS allocates the transport CID to the MS for use in transmission/reception of service data. The connection of the service is identified by the transport CID as long as the service continues. Unlike the primary management CID and the basic CID, the transport CID is allocated on a service basis each time the MS requests a service. Hence, in the case where the MS requests a plurality of services simultaneously, such as voice call, video, and Internet browsing, the MS can be allocated a plurality of transport CIDs. On the other hand, the primary management CID and the basic CID are allocated to the MS on a one-to-one basis.
The multicast CID is used to multicast the same data to a plurality of MSs simultaneously. When the BS sends data using the multicast CID, the MSs to which the multicast CID was allocated receive the data, considering that the data are for them.
A description will be made of messages involved in the initial ranging process.
Table 2 below illustrates the structure of the RNG-REQ message sent from the MS to the BS.
TABLE 2SyntaxSizeNoteRNG-REQ_Message_Format( ) { Management Message Type=48 bits Downlink Channel ID TLV Encoded Information {VariableTLV specific SS MAC Address Requested Downlink Burst Profile8 bits MAC Version Ranging Anomalies AAS broadcast capability }}
As noted from Table 2, the RNG-REQ message includes a plurality of Information Elements (IEs). Management Message Type is set to 4, indicating that the transmitted message is RNG-REQ. SS MAC Address is the MAC address of the MS, identifying the MS. Downlink Channel ID indicates the downlink channel on which the MS has received the UCD message providing uplink channel information. Requested Downlink Burst Profile is divided into bits 0 to 3 and bits 4 to 7. A Downlink Interval Usage Code (DIUC) is written in the bits 0 to 3 to request formats for transmission/reception of physical channel signals (e.g. a modulation type and an error correction type), and four Least Significant Bits (LSBs) of Configuration Change Count in the UCD message referred to in order to request ranging is filled in the bits 4 to 7. That is, the BS sends a predefined physical channel signal to the MS referring to the information provided in the bits 0 to 3 of Requested Downlink Burst Profile. MAC Version indicates a MAC version that the MS will use. Ranging Anomalies indicates whether the MS transmits at a maximum power level or at a minimum power level to attempt an access to the BS. Besides, Ranging Anomalies can be used to carry a response to an instruction regarding the increase or decrease of transmit/reception power to correct the transmit/reception power and time information of the MS during the initial ranging. AAS broadcast capability indicates whether the MS can receive a broadcast message or not.
Table 3 illustrates the structure of the RNG-RSP message sent from the BS to the MS.
TABLE 3SyntaxSizeNoteRNG-RSP_Message_Format( ) { Management Message Type=58 bits Uplink Channel ID TLV Encoded Information {VariableTLV specific SS MAC Address6 Downlink Operational Burst Profile2 Primary Management CID2 Basic CID2 Ranging Status41 = continue2 = abort3 = success4 = rerange Timing adjust4 Power level adjust1 Downlink frequency override4Center frequencyat which MS redoesinitial ranging }}
Referring to Table 3, the RNG-RSP message includes a plurality of IEs. Management Message Type is set to 5, indicating that the transmitted message is RNG-RSP. SS MAC Address is the MAC address of the MS to receive RNG-RSP. Downlink Operational Burst Profile is a response to the MS-requested downlink burst profile, i.e. a DIUC to be used in the BS. Primary Management CID and Basic CID are CIDs that are allocated to the MS and kept for connection management between the BS and the MS while the MS receives a service after ranging. Ranging Status (1 to 4) is a response to the MS's ranging request. If Ranging Status is 1, this implies that the BS directs the MS to continue ranging. If Ranging Status is 2, this implies that the BS directs the MS to discontinue ranging. If Ranging Status is 3, this implies that the ranging is successful. If Ranging Status is 4, this implies that the BS directs the MS to retry ranging. Timing adjust provides information for correcting the timing of the MS and Power level adjust provides information for correcting the transmit/reception power of the MS. Downlink frequency override indicates the frequency of another channel on which the MS will attempt initial ranging, if Ranging Status is set to 2, indicating abort.
As noted from Table 3, the MS is allocated the primary management CID and the basic CID during the initial ranging process.
Since signaling is carried out between the BS and the MS via a direct link, a highly reliable radio communication link can be established between them in the typical BWA communication system illustrated in FIG. 1. However, due to the fixedness of the BS, a wireless network cannot be configured with flexibility. As a result, the BWA communication system is not effective in providing communication services under a radio environment experiencing fluctuating traffic distribution and great change in the number of required calls.
This drawback may be overcome by applying a multi-hop relay data transmission scheme using fixed Relay Stations (RSs), mobile RSs, or general MSs to general cellular wireless communication systems such as the IEEE 802.16e communication system.
The multi-hop relay wireless communication system can rapidly reconfigure a network according to a changing communication environment and can enable efficient operation of the whole wireless network. It can expand cell coverage and increase system capacity. In the case where the channel status between the BS and the MS is poor, an RS is installed between them so that the resulting establishment of a multi-hop relay path through the RS renders the available radio channel to the MS better. With the use of the multi-hop relay scheme at a cell boundary where the channel status is poor, high-speed data channels become available and the cell coverage is expanded.
The configuration of a multi-hop relay BWA communication system designed to expand the coverage area of the BS will be described below.
FIG. 2 illustrates the configuration of a multi-hop relay BWA communication system designed to expand the coverage area of the BS.
Referring to FIG. 2, the multi-hop relay BWA communication system includes a BS 210 for managing a cell 200, a plurality of MSs 211 and 212 within cell 200, a plurality of MSs 221, 222 and 223 managed by BS 210 but located in an area 230 outside cell 200, an RS 220 for providing a multi-hop relay path between BS 210 and MSs 221, 222 and 223. Signaling is performed in OFDM/OFDMA among BS 200, RS 220, and MSs 211, 212, 221, 222 and 223.
Although MSs 211 and 212 within cell 200 and RS 220 can communicate directly with BS 210, direct communication is not available between BS 210 and MSs 221, 222 and 223 outside cell 200. Therefore, RS 220 covering area 230 relays signals between BS 210 and MSs 211, 222 and 223. Thus MSs 221, 222 and 223 exchange signals with BS 210 via RS 220.
However, individual transmission of a transport CID and data from the BS to each of MSs through the same RS requires as many management messages.
Accordingly, a CID management apparatus and method are needed which reduces the management messages sent through the RS for data transmission to the MSs via the RS and thus saves bandwidth.
That is, there is a need for a CID management apparatus and method that efficiently manage data destined for the RS and data to be relayed to the MSs through the RS by use of a CID during communications between the BS and the RS in the multi-hop relay BWA communication system.